JS - How to find the index of deepest pair of parentheses?

Question

I have a string: "5 * ((6 + 2) - 1)" I need to find the deepest pair of parentheses and their contents.

I've googled a lot and I can't find anything specific to finding the index. A lot of solutions found how many levels there are, and things like that, but nothing was really helpful. I was thinking of counting the layers, and then using a loop to solve and repeat solving until done, but it seems like this would be really slow.

I have no idea where to start, so I haven't written any code yet.

I want a function to return 5, the string index of the deepest set of parentheses. I also need to do the same for the deepest ")", since I need the pair. Example:

const deepestPair = (str) => {
    // Find deepest pair of parentheses
}
deepestPair("(2(5)4)(3)") // Returns [2, 4], the indexes of the deepest open/close parentheses

Answer 1

You could check opening and closing parentheses and use a counter for getting the most nested indices.

const deepestPair = str => {
    var indices,
        max = 0,
        count = 0,
        last;
    
    [...str].forEach((c, i) => {
        if (c === '(') {
            last = i;
            count++;
            return;
        }
        if (c === ')') {
            if (count > max) {
                indices = [last, i];
                max = count;
            }
            count--;
        }
    });    
    return indices;
}

console.log(deepestPair("(2(5)4)(3)")); // [2, 4]